Metal dispersions



United States Patent METAL DISPERSIONS No Drawing. Application December 23, 1954 Serial No. 477,383

s Claims. c1. 52-5 This invention relates to metal dispersions and, impairticular, is concerned with dispersions of metals other than alkali metals having thixotropic properties. c

It has long been known that metals, especially thealkali metals, can be dispersed in liquids in a state of very fine subdivision. Briefly, these dispersions comprise finelydivided alkali metal suspended in an inert liquid dispersion medium. Dispersions of metals other than the alkali metals have also been known, particularly in their use as paints. It is likewise-known that finelydivided metals, for example, magnesium suspended in a jet fuel, can be employed for improving combustion in the after-burners of jet engines. Because of the high density of the finelydivided metals other than the alkali metals and their higher melting points, it is difficult to obtain a suspension of the metal wherein the distribution ofthe metal can be retained over extended periods of time. .When employing these metals as adjuvants to the after-burners of jet engines, itis desirable that the metal be uniformly distributed in the fuel, easily handled, and essentially nonscttling. As a result of our work in this field, we have discovered novel dispersions of the finely-divided metals other than alkali metals which overcome the abovejand other disadvantages of the prior art and provide improved metal dispersions.

It is, therefore, an object of the present invention to provide improved dispersions of metals other the alkali metals. A particularobject isto provide dispertropic properties.

still do not settle at the higher temperatures. A still further object is to, provide novel dispersions of metals ideally suited as fuels or additives-to fuels for theafter-burners of jet engines. Other objects will be apparent from the discussion hereinafter. p

The above and other objects are accomplished by pr oviding a dispersion of finely-divided metal other than alkali metals in a substantially inert liquid organic medium which contains between about 0.03 to 0.0005 part by weight of a gelling agent, especially a polymeric gelling agent, per partby weight of the metal and a dispersing agent; The metals contemplated as a part of' the composition of this invention' :are those of groups IB, II through VII A and B, and VIII of the periodic'chart of forccomplete combustion, since these are most practical for use in afterwburners of jet engines. "Generally, the

particletsize "of the *metal will average less Zthan about 100 microns ia'ndzpreferably less thanlabout 20 microns, since vsions which are in the form of pastes or gels having thixo 7 Another object is to provide novel" metal dispersions having thixotropic properties which are stable to settling, become fluid at higher temperatures, and

. 2,927, 49 l atenteclMar. 8, 1960 the latter and smaller particle sizes are more reactive forms of the metal. Best results are achieved when the proportion of the polymer in the dispersion is between about 0.0005 to 0.02 part per part by weight of the metal. An especially preferred composition of this invention comprises a dispersion of finely-divided boron, aluminum, or magnesium coated with athin film of an alkali metal of average particle size less than 20 microns in an inert liquid hydro-carbon medium, especially a jet fuel, and containing between about 0.0005 to 0.02 part by weight of an ethylene polymer of molecular weight of at least 588 per part by weight of the coated metal and between about 0.1 to 5 percent by weight of a dispersing agent as, for example, oleic acid. The alkali metal-coated metals are of particular advantage since in the after-burners of jet propulsion devices there is only a very shortperiod of time in which the powdered metal ignites. The thin coating of alkali metal enhances ignition of the metals compared to that obtained when a suspension of the metal not coated with the alkali metal is used.

The compositions of this invention have the particular advantage of being gels or pastes which are thixotropic at room temperature. In addition to providing nonsettling of the finely-divided particles during storage, the thixotropic characteristic of these compositions is .Of particular'advantage over the previously known dispersions in that the reactivity of the metal is unretarded and these dispersions become morefluid with increasing agitation.

Thus, they are practical for the usual chemicalreactions oi the metal and more easily handled. Further, by lilvdicious choice of the polymer incorporated in the composition and the amount thereof, dispersions having parttcu- 1 lar pouring temperatures are obtained. That is, the (115- persion will be a gel or a paste at ordinary temperature but upon either agitating or heating to elevated temperature it will become fluid. These characteristics of the dis persions make them ideally suited as fuels or additives to fuelsof jet propulsion devices- Thus, wehave provided improved dispersions of finely-divided metals which retain the maximum reactivityof the metal, have uniform'distribution, and which are fluid under the condi tions of use to which they are to be employed.

As stated above, the metals which are employed in the precious metals, such as gold, silver, platinum, and the like; or mixtures or alloys thereof. Still other metals,

metalloids, mixtures, or alloys will be evident to those skilled in the art.

are those having a heat of combustion of at least 8000 B.t.u. per poundand require at least 2000 B.t.u. per pound of air for complete combustion, since these are 3 the more practical metals for use in the after-burners of jet propulsion devices, Elements having lower heats of combustion can be employed for this and other uses butzf are not as satisfactory in jet, use since the energy obtained from a practical amount of fuel would be too small.

films, the especially preferred metals are aluminum,

beryllium, magnesium, titanium, and the metalloids silicon-and boron.

ergy contentsand availability. These metals form the core of=the metals in our compositions but it is to be unthe: core metal'is reduced by such coating. Advantage The metals or metalloids which we particularly prefer Of these, aluminum, boron, and magnesium are preferred because of their high combustion enbeen found to be most practical.

'the criteria mentioned above. drocarbons, they can be selected from the group consisting of the various alkanes, alkenes, cyclanes, cyclenes, and aromatic compounds, including the mononuclear aro- 'matic compounds, polynuclear non-fused ring and polybranched chain isomers.

can also be obtained when alkali-metal-containing alloys or mixtures of sodium, potassium, and calcium and the like are employed as the coating metal. Alkaline earth metals, namely, barium, calcium, and strontium, may also be used with some degree of success. Generally speaking, the film surrounding the metallic particles of my compositions should be from about 0.001 to about 0.1 micron in thickness.

The concentration of the metal or mixtures thereof can be varied from trace amounts up to about 85 percent by weight. The preferred concentration employed is between about 30 to 65 percent by weight since these have The particle size of the metal content of the composition can likewise vary over a wide range up to about 1000 microns. The more ,reactive form of the metal in the dispersion is that in persions, it is advantageous to employ liquid dispersion media which have boiling points above the melting point of the metal. Dispersion media having boiling points be- -low the melting point of the alkali metal can be employed but generally are not preferred since these require the use of pressure in preparing the dispersion.

Among the dispersion media which we have found to be suitable are the hydrocarbons and the ethers having When we employ the hynuclear fused ring aromatic compounds, or mixtures thereof. Typical examples of the alkanes which we employ include heptane, octane, nonane, and the like, up to and including about octadecane and the like, and their various branched chain isomers. Among the alkenes are included, for example, heptylene,'octylene, and the like,

up to and including about octadecylene and their various When we employ cyclanes as dispersion media, we employ, for example, cycloheptane, cyclooctane, methylcyclohexane, dimethylcyclohexane, .isopropylcyclopentane, and the like. Typical examples of the cyclenes which we employ as dispersion media include cycloheptene, cyclooctene, l-isopropylcyclopentene-l, lmethylcyclohexene-l, and the like. Similarly, various polycyclanes and cyclenes are employed as, for example, cyclopentylcyclopentane; (2-methylcyclopentyl)-cyclohexane; cyclohexylcyclohexane; decahydronaphthalene; 1,1- dicyclopentenyl; 2,2-dicyclohexenyl; 0,4,4-bicyclodecene- 1; decahydrofluorene; and the like. Typical examples of mononuclear aromatic compounds include toluene, ethylbenzene, the xylenes, 1,2-diethylbenzene, cyclopropylbenzene, the cymenes, and the like. When the dispersion media are polynuclear non-fused aromatic compounds, we employ, for example, 1-methyl-2-phenyl benzene; 1,3-diphenylpropane; 1-phenyl-2-p-tolylethane; 1,1-diphenylheptane; and the like. When we employ polynuclear fused ring aromatic compounds, they can be, for example, indane; l-methylindane; indene; tetralin; 1,2-dihydronaphthalene; octanthrene; lmethylnaphthalene; and the like.

When the dispersion media which we employ are the ethers, they can be selected from the group consisting of the monoalip'hatic, mixed aliphatic, monaromatic, alkyl aryl and the aralkyl alkyl ethers. Typical examples of the monoaliphatic ethers which we employ are di-n-vbutyl be evident to those skilled in the art.

di-n-heptyl ether, didodecyl ether, dioctadecyl ether, and the like. When we employ mixed aliphatic ethers, they can be, for example, n-amylmethyl ether, tert-amylethyl ether, n-butylisopropyl ether, ethylisoamyl ether, nbutyln-propyl ether, and other straight or branched chain ethers which are derived from mono or poly alcohols of the alkane, alkene, cyclane, and cyclene series. When we employ monoaromatic ethers, we can employ, for example, dibenzyl ether, diphenyl ether, and the like. The alkyl aryl ethers which we employ include, for example, methylphenyl ether, methyl-o, m, or p-tolyl ether, ethyla-naphthyl ether, isoamyl-a-naphthyl ether, and the like. The alkaryl alkyl ethers which we employ are, for example, benzylmethyl ether, benzylethyl ether, benzyl-nbutyl ether, and the like. It is to be understood that poly ethers can also be employed as, for example, ethylene glycol ethylmethyl ether; 1,4-dioxane; pyrocatechol dimethyl ether; 'resorcinol dimethyl ether; and the like.

The foregoing is merely a representative list of the dispersion media which we employ. Other examples will It is to be likewise understood that mixtures of the various dispersion media can be employed as, for example, mixtures of the hydrocarbons including kerosenes, heavy alkylates, petroleum distillates, jet fuels, and the like, and mixtures of ethers and mixtures of ethers and hydrocarbons and the like. The dispersion media which we particularly prefer are those which are liquid at room temperature. Likewise, the liquid hydrocarbons, particularly those containing between about 7 to 18 carbon atoms, are best suited for the preparation of the compositions of this invention.

A wide choice of the polymer to be employed in the compositions of our invention can be made. It is preferable that the polymer be of limited solubility in the dispersion medium at ordinary temperatures or be substantially insoluble in the medium at room temperature at the concentration employed. Thus, the polymer to be employed will depend upon the dispersion medium employed. Ordinarily, the choice of polymer is such that it is essentially insoluble in the dispersion medium when in concentration between about 0.0005 to 0.03 part by weight of metal. A further criterion of choice of the polymer is that it have an average molecular weight above about 600. Likewise, the polymer employed should comprise only the elements, carbon, hydrogen, and oxygen, and preferably only carbon and hydrogen since these exhibit lesser reactivity with the metals. Thus, among the polymers which we can employ having the aforementioned characteristics are polyethylene, polystyrene and the alkyl styrene polymers,polyisobutylene and butyl rubber, polybutadiene and co-polymers thereof, natural rubber, polyisoprene, hydrogenated polybutadiene, and the like hydrogenated polymers, coumaroneindene resins, poly ethers of the carbowax-type, polyacrylates and methylacrylates, polyvinyl ethers, poly esters, methyl and ethyl cellulose, cellulose acetate, and the like. The foregoing is a representative list of the polymers which we employ and, consequently, other polymers will be evident to those skilled in the art.

As stated previously, the proportion of the polymer is not greater than about 0.03 but not less than about 0.0005 part by weight of polymer per part by weight of metal. Best results are obtained when the proportion of polymer is between about 0.0005 to 0.02 part by weight per part by weight of metal. Concentrations not within these ranges should be avoided since the reactivity of the metals will be retarded at higher concentrations and at lower concentrations the desired characteristics of the dispersion are not obtained. A polymer which we have found to be especially suitable is polyethylene having an average molecular weight greater than 588. In general, the amount of polymer employed will depend upon its molecular weight; thatis, as the molecular .weight increases,

ether, di-sec-butyl ether, diisobutyl ether, di-n-amyl ether, the amount of the polymer required decreases.

A wide selection of dispersing agents canhe employed in the composition of our invention.-v mon'g suchagents arefinclud'ed the high molecular weight acids; tor ex.- ample, hexo'ic acid, octoic acid, capric acid, lauric acid, myristic acid, stearic acid, palmitic acid and their salts. Likewise, various alcohols can be employed as, for example, n-hexyl'alcohol, n-octyl alcohol, cetyl alcohol, cyc'lohexa'nol, Phenol, Z-ethyl hexyl alcohol, and the like. Additionally,.the hydroperoxides can be employed which include, for example, tetralin hydroperoxide, tert-butyl hydroperoxide, decalin hydroperoxide, tert-amyl 'hydroperoxide, and thelike. 5 Other dispersing agents which can be employed include metal salts of fatty acids, carbon black,

and yarious ethers. }The' foregoing is merely a representat'ive' list of the dispersing agents which. are employed. The dispersing agents which we particularly prefer are the high molecular weight acids or their salts, especially oleic acid. These dispersing agents maintainsuspension of .the metal particles when the composition is fluid and prevent agglomeration at higher, temperatures, The amount of dispersing agent employedis generally 0.01 to 5 percent of the total weight offthe dispersion. In some instances,

more or less than this quantity can be employed to equal advantage. e

The general technique which we employ in the preparation of these dispersions is to first obtain the metal in powdered form of desired particle size. These metals and .metalloid powders are prepared by methods involving ab,-

rasion, grinding, or milling, or may befobtained by chem- "ical' means, such as alkali metal reduction of the metal salts. The metal powder is then fed 'to the dispersion medium and vigorously agitated at a temperature pref erably between about 50 and 150 C. with the dispers- King agent and polymerfbeing'added during agitation. Temperatures higher than150 C. can'be employed but are not required. Temperatures below about 50 C. should be avoided since agitation becomes more difficult. When a dispersion of these metal powders coated with an .alkali or alkaline earth metal is desired, the metal powder is first agitatedwith a proportionate part of the alkali or alkaline earth metal at a temperature above the melting point of the coating metal employed. The mixture is then cooled and dispersed in the dispersion medium as described above.

The dispersing agent can be added to the original mix- 1 tube or during the course of agitation. The polymer can likewise be added at any' time during the course of the preparation of the dispersion. However, best results are obtained if the polymer is added near the end of the agitation cycle, as for example, about 5 minutes prior to the completion of the agitation. Adding the polymer at the beginning of the. preparation of the dispersion .or,,in other words, in'the original dispersion mixture is not de- "sirafble since the dispersion 'wi-ll coagulate and hinder efrfic'ient agitation. Adding the polymer in the latter stage of the period of'agitation permits one to avoid preheating the. polymer and also to achieve the most efl'icient agitation in the preparation of uniformly dispersed metal dispersions eontaining the polymer.

To further i-llustrate the compositions .ofthis invention and their preparation, the following examples are pre-' sented whereinlunless otherwise specified, all parts are by weight. I

Example I To a reaction vessel equipped with heating means, agitating means and a means for maintaining an inert 1 atmosphere is added 200parts of magnesium-having an p 5 minutes. The agitation isstoppcd and the, mixture'is Example II The procedure of Example I is repeated using 200 parts of boron of average particle size of 10 microns, and 1 part by weight of polyethylene. After adding the polyethylene the agitation period is about 30 minutes. Upon cooling the dispersion transforms to a gel. The fluidity of the dispersion is increased upon mild agitation at room temperature. Upon heating to 85 C., the dispersion becomes fluid. This dispersion is stable to settling when left standing over a period of 5 months. 7

Example III The procedure of Example I is repeated except that 200 parts of powdered titanium having an average particle size of about microns is employed. A dispersion hav- 1 7 ing essentially the same characteristics as that obtained in Example I is produced.

' Example IV .To 200 parts of substantially anhydrous gas turbine engine fuel having a 10 percent evaporation point of 250 F. and an endpoint of 535 F., a specific gravity at F. of 0.810, a freezing point of F., and a heating value of 18,650 B.t.u. per pound is added 200 parts of finely-divided magnesium having an average particle size of 20 microns. The mixture is agitated and heated to a temperature of 100 and to this mixture is added -6 parts of polyethylene of average molecular weight of 25,000 and 1 part oleicacid. Agitation is continued for an additional period of 15 minutes. Upon completion of agitation the mixture is cooled to room temperature. 'The dispersion obtained is thixotropic with the magnesium uniformly dispersed and is suited as a fuel in the afterburner of jet propulsion devices, either as obtained or, if desired, further diluted by a jet fuel.

Example VI 7 Employing the procedure of Example V a similar thixo Erample VII A homogeneous dispersion of finely-divided aluminum is obtained when 100 parts aluminum of 30 micron average particle size, 200 parts toluene, 2 parts stearic acid, and 3 parts of polystyrene of average molecular weight of 30,000 are employed.

Example VIII In this composition. finely-divided boron coated with sodium is to be dispersed. The procedure is as follows: Employing the same equipment. as described in Example I above, about parts of finely-divided boron of 10 micron average particlegsize are added to the reaction vessel- While: maintaining the'system under an atmosv some phere of dry nitrogen, about 10 parts of metallic sodium are added and the temperature is raised to 100 C. The mixture is then agitated for about minutes to form a film of sodium substantially surrounding the boron particles. Next, 200 parts of xylene and 1 part of oleic acid are added thereto. Agitation is continued for an additional period of minutes and then 0.05 part of polyethylene having an average molecular weight of about 25,000 are added to the mixture. Agitation is stopped about 5 minutes after adding the polyethylene and the mixture is cooled to room temperature. The dispersion thus formed is a homogeneous mixture having thixotropic properties.

Example IX A similar dispersion is obtained when operating essentially as described in Example VIII and substituting a jet fuel, such as JP-3, IP 4, JP-S and the like jet fuels, for xylene in the above example. The fuels prepared in accordance with this example are eminently suited for use as after-burner fuels and the increase in thrust is materially improved compared to that obtained when jet fuel with a magnesium suspension not coated with sodium is used.

Equally good dispersions are obtained when the othe metals described previously are substituted for the metals employed in the above examples. Likewise, the various dispersion media previously described, particularly the liquid hydrocarbons, can be substituted in the above examples and the other previously described polymers can also replace the polymers in the above examples. In addition, the various other dispersing agents previously mentioned can be used to equal advantage. It will be evident that many combinations of the metal, dispersing medium, dispersing agent, and polymers can be made to provide a dispersion which is a gel at room temperature having thixotropic characteristics.

Although the above discussion has been limited to polymers as gelling agents to provide the thixotropic properties of the compositions of this invention, other gelling agents which provide thixotropic dispersions will be evident.

The compositions of our invention can be employed in other uses than as 'fuels in the after-burners of jet propulsion devices. Generally speaking, they are useful power for ram-jet engines. Still other uses will be evident to those skilled in the art.

Having thus described the novel compositions of this invention and the method of their preparation, it is not intended that it be limited except as described in the appended claims. 1 r

We claim:

l. A thixotropic composition consisting of finely divided metal selected from the group consisting of magnesium, boron, titanium, and aluminum dispersed in a 5 normally liquid hydrocarbon substantially inert to said metal, a dispersing agent selected from the group consisting of high molecular weight fatty acids, monohydric saturated alcohols containing from about 6 to 16 carbon atoms, and hydroperoxides selected from the group consisting of tetralin hydroperoxide, ter-t-butyl hydroperoxide, decalin hydroperoxide, and tert-amyl hydroperoxide, and between about 0.0005 to 0.03 part by weight per part of said metal of a polymer selected from the class consisting of polyethylene, polystyrene and polyisobutylene, the polymer having an average molecular weight above about 600.

2. A thixotropic composition consisting essentially of fiinely divided metal selected from the group consisting of magnesium, boron, titanium, and aluminum coated with a thin film of alkali metal and dispersed in a normally liquid hydrocarbon substantially inert to said metal, a dispersing agent selected from the group consisting of high molecular weight fatty acids, monohydric saturated alcohols containing from about 6 to 16 carbon atoms, and hydroperoxides selected from the group consisting of tetralin hydroperoxide, tert-butyl hydroperoxide, decalin hydroperoxide, and tert-amyl hydroperoxide, and between about 0.0005 to 0.03 part by weight per part of said metal of a polymer selected from the class consisting of polyethylene, polystyrene and polyisobutylene, the polymer having an average molecular weight above about 600.

3. The composition of claim 2 wherein said dispersing agent is a high molecular weight fatty acid and said polymer is polyethylene.

4. A thixotropic composition as defined in claim 2 wherein said metal is coated with a thin film of sodium and wherein said dispersing agent is oleic acid present in an amount between about 0.1 to 5 percent by weight of said composition.

5. The composition of claim 4 wherein said metal is magnesium.

6. A thixotropic composition consisting of about 200 parts by weight of finely divided magnesium having an average particle size less than about 20 microns dispersed in 200 parts by weight of kerosene, 2 parts by weight of oleic acid and 5 parts by weight of polyethylene having an average molecular weight of about 20,000.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Gregory: Uses and Applications of Chemicals and Related Materials, vol. I, Reinhold Publishing Corp.,

New York, NY. (1939), page 420. 

1. A THIZOTROPIC COMPOSITION OCNSISTING OF FINELY DIVIDED METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, BORON, TITANIUM, AND ALUMINUM DISPERSED IN A NORMALLY LIQUID HYDROCARBON SUBSTANIALLY INERT TO SAID METAL, A DISPERSING AGENT SELECTED FROM THE GROUP CONSISTING OF HIGH MOLECULAR WEIGHT FATTY ACIDS, MONOHYDRIC SATURATED ALCOHOLS CONTAINING FROM ABOUT 6 TO 16 CARBON ATOMS, AND HYDROPEROXIDES SELECTED FROM THE GROUP CONSISTING OF TETRALIN HYDROPEROZIDE, TERT-BUTYL HYDROPEROZIDE, DECALIN HYDROPEROZIDE, AND TERT-AMYL HYDROPEROZIDE, AND BETWEEN ABOUT 0.0005 TO 0.03 PART BY WEIGHT PER PART OF SAID METAL OF A POLYMER SELECTED FROM THE CLASS CONSISTING OF POLYETHYLENE, POLYSTYRENE AND POLYISOBUTYLENE, THE POLYMER HAVING AN AVERAGE MOLECULAR WEIGHT ABOVE ABOUT
 600. 